This is a discussion on High Altitude Turbo study within the High Altitude Tuning forums, part of the Engine Modifications category; So in the absence of answers I have decided to ask the audience, knowing I will get votes on every ...

High Altitude Turbo study

So in the absence of answers I have decided to ask the audience, knowing I will get votes on every answer. Hopefully I can tell which answer is the loudest.

At high altitude we have a unique problem. My 2.5L STI behaves more akin to a 2.0L EVO than a sea level STI. I made the mistake/choice to overboost my VF39 to 19-20 psi. At 5500 ft, this is a pressure ratio of 2.6-2.7, which is out of the range of the only noncompressor unmap that is available online. I now am blowing smoke worse than Cheech and Chong.

Since altitude robs flow but allows higher boost due to lower absolute manifold pressure, I want to find a turbo that won't surge and allows high PR, preferably with ball bearings.

My input conditions-
2.7-3.0 PR boosting between 3000 RPM and redline.
Depending on the calculation that is between 15 lb/min and 39-42 lbs/min.

I have looked at the 68HTA and PE1818 posts, but without information (compressor map) I won't spend the money.

Does anyone know any others that will fit this range? Please don't say 18-20G FPGreen etc. If it is too big for the altitude, I might as well walk than wait for the spool.

Also, I'd like to know if anybody has found a T04E super 50 bolt on turbo for a Subaru. There doesn't seem to be one available anywhere. I don't really have $4k to spend on a rotated mount, and I definitely don't want an FMIC.

So it turns out the GT3071R is not available with a 0.63 A/R for stock location bolt on. The GT2871R 52 trim only exists as the APS SR40. The Evo 3 16G is inefficient and not ball bearing. The FP 68HTA has no published information other than a couple of miscellaneous dyno charts and teh f45t3r claims of XYZ whp using E85 costworth engines and huge FMICs, and threads with more trolls than Warcraft and the library combined. So, thank you for not posting. Nothing better than skiing in untracked snow.

I don't think I can upload an Excel file, so I'll paraphrase. At a Pressure Ratio of 2.0 flow is 11.3 lbs/min at 2500 rpm, 17.7 at 4k, 30 at 7k. At 2.5, 15 at 2.5k, 21 at 4k, 37 at 7k. At 2.7, 17 at 2.5k, 21 at 4k, 39 at 7k. At 3.0, 19 at 2.5k, 25 at 4k, 43 at 7k. All of these calculated at hot temps, so allow more flow for cold air. The main thing is getting a small enough turbine that the VF39 lag is improved, with ball bearings for durability.

So I've placed an order for an APS SR40, $1699, with a 0.6 A/R. Ball bearings, almost the same as a GT2871R 52 trim. 75% efficiency around 2.7 PR (vs. 71% for Evo 3 16G).

I give it a 50/50 chance of actually happening. Between the vendors who tried to sell me GT28RS (way too small and low PR only) with outright lies "it's a GT2876R", the couple selling random named mishmash turbos with unknown capabilities and no promises, and the vast majority remaining "you want an FP green/GT35R/rotated turbo mount/huge FMIC just sign the blank check now" I can't wait to be done with this. My favorite response, "why would you want only 350 whp?".

Sorry I missed this. I've been curious for a while as to what would make a good high(ish) elevation turbo but for a 2.0. Please let us know how things work and enjoy the fresh tracks. Wish I could get back to CO for some powder days sometime soon.

"From a little spark may burst a mighty flame." - Dante
"The stitch is lost unless the thread is knotted." - Italian proverb

Sorry I missed this. I've been curious for a while as to what would make a good high(ish) elevation turbo but for a 2.0. Please let us know how things work and enjoy the fresh tracks. Wish I could get back to CO for some powder days sometime soon.

I would recommend the 19T upgrade for the 2.0L at higher elevations. Check out its compressor map sometime, and you'll see that it does really well at high pressure ratio's (esp in the higher revs). The small TD04L hot side will help spool in thin atmosphere and won't really hinder your performance much because...well...the air is thin and there's less of it!

Right now on NASIOC we have a thread going in depth on the 19t upgrade, and a couple of people have responded with hard data. The results look pretty good to be honest. In the higher revs the 19T actually likes higher Pressure ratio's than the small 16G FWIW.

VVVV:

On the 2.5L I'm not sure what would be good. Something makes me think the HTA68 would be good because of its TD05 hotside, and the fact that the compressor wheel is slightly larger than a 20G if I remember correctly.

Your going to have a hard time finding a turbo that can support 3.0 pressure ratio (for any decent length of time), that will spool quick enough for your needs. You need to be a bit more realistic. A pressure ratio 2.5 will get you ~18 psi depending on the changing weather. 18 psi on an HTA68 would still be rocking pretty good. If you combine that with an oxygenated fuel like E85, then you'll be rolling in the power.

The third run was after having a battery charger on it for a while, though cylinder 2 was tested first, so it may have already run down by the time I did the others. This is with an atmospheric pressure reading of 10.8 psia.

xsnapshot - I did look at the 19T map while shopping. It kind of ran out of flow before the engine would. I didn't want to choke out the top end too soon. The 68HTA had lots of great threads debating it left and right, but since no compressor map exists, I wasn't about to spend $900 on anything sight unseen. Plus, I really wanted ball bearings. I'm willing to spend twice as much if it means the up front information and long term durability are there. I'm definitely not impressed by the VF39 center cartridge.

So I got the SR40 (with 0.6 A/R turbine) turbo installed (not "stock" - required some stretching of hoses beyond their normal positions, so future mods like IC hose and turbo inlet are needed to clean it up). I put some preliminary tuning mapped in. The first run just messing around I "accidently" boosted to 20.5 psi (I did know what I was doing, and still only hit the 90 MAP column on my previous tune). I have since turned down the boost for regular situations, and worked on the spool. I am now getting 18 psi boost by 4000 rpm, but not only am I seeing a PR of 2.0 by 3500 RPM, but the turbo holds almost a 2.5 PR to redline (~16.5 psi). I am still working on the maps a lot to try to get ready for the rallycross this weekend. Even at peak boost I am running around 11.0:1 AFR due to the high efficiency compressor. So far things look really good.

I might get some dyno time for testing maps, but I probably won't post them. Homie don't play that game.

I would never have recommended the 19T to anyone having the 2.5L, even at that altitude.

Your spool up sounds pretty good for the size of that turbo, and the altitude your running at. I'm actually surprised you got it spooling up that quick.

a 2.0 PR for you is what? Like 11 psi? What are you running for boost control? You might get another 200 RPM quicker spool with an MBC. However you would loose the ECUs ability to lower the boost targets with decreases in atmospheric pressure.

So does anyone know aprox how much power do you loose with high alt? Where I live is about 4300

A stock STI in denver was at about 180 HP raw on a dyno, if my memory is correct (which is seldom is). We lose about 40-50 HP.

Sorry Xsnapshot, I don't read good. I's smart like a model. I'm calling 12 psi a PR of 2.0, even though I know 11 psi is probably more realistic. I don't like to admit I have that big of a high problem.

I can't take credit for the spool. That's a result of buying the 0.6 A/R turbine version of the SR40. The stock STI boost controller does well enough for my needs.

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